The present invention pertains to a hardenable or cross-linkable fluorinated copolymer of chlorotrifluoroethylene (C.sub.2 F.sub.3 Cl), tetrafluoroethylene (C.sub.2 F.sub.4), a nonhydroxylated vinylic ether and an allylic polyol. This copolymer is soluble in organic solvents and is particularly recommended for the fabrication of paints and varnishes.
The fluorinated polymers are known for their good mechanical properties and their excellent resistance to chemical products and weather. However, their lack of solubility in conventional solvents prevents their use for certain applications such as resins for coatings such as paints and varnishes where their properties are desired for the production of coatings and good resistance and easy maintenance.
In order to take advantage of the properties of the fluorinated polymess while avoiding their drawbacks, attempts have been made to make them soluble in the conventional organic solvents. In order to accomplish this, it is known to diminish the crystallinity of the fluorinated polymers by copolymerization of ethylenically unsaturated monomers, at least one of which is fluorinated. In addition, for the use of these copolymers it is desirable for certain applications, particularly when employing them in the fabrication of paints and varnishes, to preserve a sufficient degree of rigidity and to make them hardenable by incorporating functional groups in their structure.
Under these conditions, homopolymers containing only C.sub.2 F.sub.4 or C.sub.2 F.sub.3 Cl are totally insoluble in the usual solvents, taking into account their capacity for crytallization. In order to make copolymers of C.sub.2 F.sub.4 or C.sub.2 F.sub.3 Cl soluble it is necessary to incorporate in the composition of the final copolymer a noteworthy amount of nonfluorinated monomer. Good solubility in conventional solvents is necessary for producing paints and varnishes with high dry extract and low viscosity in order to factiliate application.
In order to provide these copolymers with this solubility and to make them hardenable, copolymerization is carried out with at least one fluorinated monomer and one ethylenically unsaturated monomer with a functional group, usually selected to be the hydroxy group because it cross-links readily with isocyanates or melamine-formaldehyde resins.
Fluorinated copolymers based on C.sub.2 F.sub.4 or C.sub.2 F.sub.3 Cl which are soluble in conventional solvents and have hydroxy functional groups are described in French Patents 2,488,260 and 2,569,703 as well as in EP 180,962.
The copolymers described in French Patent 2,488,260 are a combination of C.sub.2 F.sub.4 and/or C.sub.2 F.sub.3 Cl with hydroxylated vinylic ethers. The level of fluorinated olefins in accordance with the technique described does not exceed 60 mole % and is advantageously about 50 mole %, taking into account the alternation of fluorinated and nonfluorinated structural units.
The copolymers described in French patent 2,569,703 are characterized by the combination of C.sub.2 F.sub.3 Cl with a vinylic ester; the functional group is provided by a monohydroxylated allylic derivative.
The copolymers described in EP 180,962 are characterized by the combination of any fluoroolefin with a vinylic ester. The functional group is provided by a hydroxylated vinylic ether.
In the last two documents, the presence of the vinylic ester is necessary to make the copolymer soluble. The amount of vinylic ester required to obtain good solubility is generally high: up to 70 and 60 mole %.
The strong tendency towards homopolymerization of the monomers of the vinylic ester type makes inevitable the presence of neighboring sequences of vinylic esters, which has a very negative impact on the aging qualities of the coatings; i.e., paints and varnishes.